Process for burning cement and similar raw material



Jan. 17, 1939. N. AHLMANN 2,143,905

PROCESS FOR BURNING CEMENT AND SIMILAR RAW MATERIAL Filed July 1, 1958INVENTOR lV/KOZ 4/ #194 MAN/V ATTORNEY5 Patented Jan. 17, 1939 UNITEDSTATES PROCESS FOR BURNING CELIENT AND SIMILAR RAW MATERIAL NikolaiAhlmann, Fredriksberg, near Copenhagen, Denmark, assignor to F. L.Smidth & 00., New York, N. Y., a corporation of New Jersey ApplicationJuly 1, 1938, Serial No. 216,895 In Great Britain July 14, 1937 8Claims.

This invention relates 'to the burning of cement, or the sintering ofsimilar raw materials, by forming a porous layer of a mixture of the rawmaterial and coke, or other solid fuel, and

5 drawing or forcing gas capable of supporting combustion through thelayer'after igniting the fuel.

Researches have shown that if cold air is drawn or forced through such alayer the burning is unsatisfactory, even if the mixture contains arelatively large quantity of fuel. This may be accounted for by the factthat the raw material, which as a rule is moistened'in order to renderthe mixture porous, must not only be burned or sintered, but also mustbe dried and preheated, and at least in the case of cement rawmaterials, mustbe calcined. All of these processes together require aconsiderable quantity of heat.

According to the present invention the amount of heat that must beproduced by the fuel per unit volume of the mixture is reduced, withoutthe'necessity of employing more than a relatively small amount ofexternal heat, by drawing or forcing heated gas through the layer to dryand preheat it and thereafter igniting the fuel and carrying on theburning or sintering process by drawing or forcing further gas throughthe layer. Preferably the gas for drying and preheating the layer isdrawn or forced transversely through the layer of material twice,namely, first through the layer at a point where the burning orsintering is complete, so that the gas is heated, and then through thelayer at a point'in advance of that at which the fuel is ignited. Theevaporation of the moisture contained in the raw material, I

and all or part of the preheating, are thus effected by means of hot gasso that the whole of the heat generated by the fuel 'is available forthe remainder of the process. With materials that must be calcined theprocess may .be so carried on that some of the calcination is alsoeffected by the hot gas. Whether the process is so carried on that onlysome of the preheating, or all a of the preheating, or all preheatingand part of the calclnation,'is effected by the hot gas, it is only asingle-stage process, in that all of the fuel that is burnt is combinedin the initial layer of raw material and fuel. It is, immaterial whether.the gas that is passed through the layer before the ignition of thefuel is-capable of supporting combustion or not. 1

When the fuel is ignited the gas must, of course, be capable ofsupporting combustion, and 5 the fuel may be ignited simply by passingthrough the layer-gas which is rich in oxygen and heated to asufliciently high temperature. Alternatively the layer may be ignited bya flame, which may be a gas or oil flame, and which need consume only asmall amount of fuel. In general, it is 5 convenient to combine the twomethods so that the amount of. heat contained in the gas passed throughthe layer is increased on passing the flame.

The gas that is passed through the layer after the ignition may simplyconsist of ordinary atmospheric air, but it is better either to addoxygen to the air or to preheat the air. Of course, hot gaseous productsof combustion may be used if they are rich enough in oxygen. Forexample, 15 the gases coming from a furnace working with a high excessair coeflicient may be used. Preferably the gas that is passed throughthe layer after the ignition is air that has first been passed throughthe layer at a point where the burning or sintering is complete.

The incoming gas that is passed through the layer where the burning orsintering is complete is preferably divided into two streams after itspassage through the layer, namely, a stream that has passed through anearlier and hotter part of the layer and a stream that has passedthrough a later and cooler part. The former stream is then passedthrough the layer a second time at a point where the ignition begins, orhas begun, andthe latter stream is passed through the layer at a pointwhere ignition has not begun and thus serves as the drying andpreheating gas.

Apparatus suitable for carrying out the process is illustrateddiagrammatically in the accompanying drawing but it will be understoodthat any appropriate apparatus capable of carrying out the process maybe used. In order that the invention may be clearly understood andreadily carried into effect one process in accordance 0 therewith willnowbe described by way of example with reference to the drawing.

a The apparatus may comprise an endless travelling grate carried bydrums 2 and 3. The grate is preferably protected from the action ofvery, hot gases by,a layer 5 of any suitable material that has alreadybeen sintered, this material being supplied from a hopper 4. The mixtureof raw material and fuel in porous form is fed from a hopper 6 onto thelayer 5 and forms thereon a top layer 1. Atmospheric air is drawnthrough a pipe 8, the end of which is shown in the drawing, and passesupwards through the grate and the layers 5 and I into passages 9 and I0,and then passes downwards through the layers and the grate into a pipe I9. During its first passage through the layer 1 the air is heated sothat that part of it which passes through the portion iii of the layerand the passage 8 and then arrives at the portion ll of the layer 1,serves to dry and preheat the material, and may even calcine it to someextent. That part of the incoming air which passes through the portionl5 of the layer 1 and the passage l passes by a flame l3 to the portion12 of the layer 1, and is hotter than that part of the air which passesthrough the passage 9, both because it is heated by the flame l3 andbecause the portion l of the layer 1 is hotter than the portion Hi. Thisair is in fact so hot that it aids the flame l3 in igniting the fuel inthe portion l2 of the layer. Burning of the fuel proceeds as the gratetravels and is complete when the rear edge of a wall [4 is reached. Thiswall is provided just above the surface of the layer I and forms onewall of the passage In so that no air passes longitudinally through thelayer'directly from the portion l5 thereof to the portion 12.

It will now be seen that one portion of the incoming air passes throughthe layer 1 at a point where the burning or sintering is complete andimmediately adjacent the burning or sintering zone and this portion ofair, which is the hotter portion, is passed again through the layer atthe ignition or burning and sintering zone. The other portion ofincoming air is also first passed through the layer at a point whereburning or sintering is complete but more remote from the burning orsintering zone and nearer to the discharge end of, the apparatus,and-this part of the air is again led through the layer in advance ofthe ignition zone to dry and preheat the incoming material.

The air thatpasses through the portions I 5 and [8 of the layer 1 coolsthe material to such an extent that both the pre-sintered and preburntmaterial in the layer 5 and the material in the layer 1 may be conducteddirectly to clinker silos or grinding machinery. The layers can easilybe separated from each other'as the material in the layer 5 remainsunchanged during the whole process and simply drops oi the rate asindicated at H, whereas the material in the layer 1 sinters together toform a compact mass which when its direction of travel is changed at thedrum 3 drops off in large lumps I 8 I claim:

1. A process for burning cement or sintering similar raw materials whichcomprises forming a porous layer of a mixture of the raw material andsolidfuel, passing hot gas through the layer to dry and preheat thematerial, thereafter igniting the fuel, and passing further gas throughthe layer by which the burning or sintering proper is carried on.

2. A process for burning cement or sintering similar rawmaterials whichcomprises forming a porous layer of a mixture of the raw material andsolid fuel, igniting the fuel, passing gas through the layer twice,namely, first through the layer at a point where the burning orsintering is substantially complete so that the gas is thereby heatedand then through the layer at a point in advance of that at which thefuel is ignited to dry and preheat the material, and

passing further gas through the layer by which the burning or sinteringproper is carried on.

3. A process for burning cement or sintering similar raw materials whichcomprises forming a porous layer of a mixture of the raw material andsolid fuel, passing hot gas through the layer to dry and preheat thematerial, and passing further gas through the layer by which the burningor sintering proper is carried on, said further gas being suificientlyrich in oxygen and heated to a sufficiently high temperature to effectignition of the fuel.

4. A process in accordance with claim 1 in which the ignition of thefuel is effected bya flame.

5. A process in accordance with claim 1 in which the gas for carrying onthe burning or sintering is preheated and rich in oxygen and ignition ofthe fuel is effected by passing said gas by a. flame and directlythereafter passing it through the layer at the point where ignition isto begin.

6. A process for burning cement or sintering similar raw materials whichcomprises forming a, porous layer of a mixture of the raw material andsolid fuel, igniting the fuel at a burning or sintering zone, passinggas through the layer at a zone where the burning or sintering issubstantially complete to cool the layer and heat the gas, and passingthe heated gas a second time through the layer at the burning orsintering zone.

7. A process for burning cement or sintering similar raw materials whichcomprises forming a porous layer of a mixture of the raw material andsolid fuel, igniting the fuel at a burning or sintering zone, passinggas through the layer at a zone where the burning or sintering issubstantially complete to cool the layer and heat the gas, and passingthe heated gas a second time through the layer in advance of the burningor sintering zone to dry and preheat the material.

8. A process for burning cement or sintering similar raw materials whichcomprises forming a porous layer of a mixture of, the raw material andsolid fuel, igniting the fuel at a burning or sintering zone, passinggas through the layer at a. zone where the burning or sintering issubstantially complete to cool the layer and heat the gas, dividing saidgas after its passage through the layer into two streams, namely, astream that has passed through the'hotter portion of the layer adjacentthe burning or sintering zone and a stream that has passed through acooler portion of the layer more remote from the burning or sinteringzone, passing the first mentioned stream a second time through the layerat the burning or sintering zone, and passing the last mentioned streama second time through the layer at a point in advance of the burning orsintering zone to dry and preheat the material.

NIKOLAI AHLMANN.

